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Hi Joel!! I didn't catch your user name 'till just now. Good to see you and your work - our paths don't cross as much as they used to.

Honestly, you got me with that airfoil.

It is very short-coupled with respect to pitch, suggesting that the CG range is going to to be very narrow. I'd hate to suggest something that's not even close to being flyable. Maybe someone else has experience with that airfoil on either a flying wing design or at least something that's very short-coupled.

Not to leave you without any input, my thoughts for a regular, slightly re-flexed airfoil are that it should be in the 4" range (+/- 1/2")... but I don't want you to use that number without someone's experience saying so.

Have you considered the 'ol trial/error method of a small foam replica to experiment with?

It is going to behave like a plank flying wing. The CG should be at about 22% MAC, and the flyable range will be very small as Gary said: too far forward and you won't have enough elevator power to slow it down to a reasonable trim speed; too far aft and it will be too pitch sensitive.

The airfoil does not make a difference to the CG location or stability (except for second order effects), only the trim.

Kevin

Edit: The second order effects can become important when you are flying with very small static stability margins (22% MAC would be about 3% SM, which is pretty small). Re effects, etc, can cause shifts in the neutral point on the order of a few percent. Normally these small changes don't make much difference, but when you have a very small static margin, they can cause significant changes in pitch stability with speed and AoA.

Your pictures of the model don't seem to match the sketch you showed in your first post.

From the sketch I'd suggest that the 20'ish% chord location would be about at the finger tips of the "hands". But your pictures suggest that the finger tips are far more back than that on the final model.

I suspect that the airfoil you chose is going to require a pretty good dose of aileron reflex since the ailerons are not very wide. And I don't see anything that is going to act like a V tail. At most you've got what appears to be some slight angle in the center section elevator. Or that could be just wishful thinking.

I'd make a small chuck glider to test things out before testing the full size ship. Looks cool, it would be a shame to get a dent in it before it's fine tuned.

why not start by lightly throwing it while kneeling on the ground? this way it won't have far to fall, or just glancing impact with the ground. If things are looking right, give it a harder toss and hopefully it will go 40 ft. (from 4ft, 10:1 glide ratio).

The KF airfoil is sturdy enough and easy to build but make larger ailerons -if you can.
and if possible make some w shaped bracing - (CF strips CA in place on bottom of aileron ) to stiffen em.
These all foam setups tend to bend easily and positive control can become vague.as speed changes

Most of the reason for the airfoil shape is to gain some rigidity.
airfoils are a compromise - strength first - shape next .
Your setup is a good compromise - but more variable -in undercamber - for slow flying may help.

Richard, I used a technigue I found in the foamiies forum to stiffen the foam. You use newspaper/and or tissue. and titebond glue to layer with. It works incredibly well and is vey light. I have no worries about this wing or ailerons warping in flight.
RTF at present without paint is 7.2 oz psf

Richard, I used a technigue I found in the foamiies forum to stiffen the foam. You use newspaper/and or tissue. and titebond glue to layer with. It works incredibly well and is vey light. I have no worries about this wing or ailerons warping in flight.
RTF at present without paint is 7.2 oz psf

Good technique -- I did a few models which were covered in silkspan and painted with Titebond- stif and strong - easy to do
I now have a box of carbon bits n pieces - rods /strips etc.- so I just stick those in the surface using a sharp knife to install.
for my teeny tiny models - lighter .